Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks for pointing me at the Octave code. I'll have to do some reading as I'm pretty sure my implementation is buggy. Regarding, the 700 bit/s mode, I do hope there will be no major change in the library version, as we have to use the distribution packaging, on stable. Thanks, Adrian

Re: [Freetel-codec2] 2400A VHF modem performance

Hi Adrian, There is Octave and C code for the mFSK modem we have developed in codec2-dev, that we have tested against the ideal FSK performance curves. Not sure I'd call it matched filter, but take a look at the code. It's important to check your modem implementation against theory at a

Re: [Freetel-codec2] why 4, and fsk, psk

If implemented correctly, 4FSK gets you 3dB over 2FSK on an AWGN channel. The FSKs can use class C PAs. For DRM/C4FSK they _are_ bandwidth constrained due to the high bit rate of AMBE/standards (which is black box with a bit rate so they have no choice over). I presume this is the reason for

Re: [Freetel-codec2] why 4, and fsk, psk

There was some neat AM designs a couple of years ago, but I think they all petered out last year. Narrow-band FM still remains king on VHF and up. I play around a little bit with an used FT-857d, but that's a Cadillac radio, and I use it mostly on HF. I think that's the problem with the current

Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks very much for the tips! Would you suggest that the matched filter approach is better for 4FSK as well? I am using it for 2FSK and it works well, it's just that being lazy I wanted to avoid too much complexity in the code for the 4FSK variant. Regarding PSK: I have several things

Re: [Freetel-codec2] 2400A VHF modem performance

On 10/5/17, Steve wrote: > You might also do your testing in a more remote spot. The use of ISM > in the city is probably pretty high, and interference would be an > issue. It might not break the squelch (spread spectrum, etc), but the > bits would be corrupted. > > I see

Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks for the answer! I have just simulated a 2FSK modem on AWGN channel, but this time without using FM demodulation. It performs just like you said, ~2 dB worse than QPSK (at 5% frames dropped). This means that the FM demodulator I used for 2400A must be introducing some symbol

Re: [Freetel-codec2] 2400A VHF modem performance

You might also do your testing in a more remote spot. The use of ISM in the city is probably pretty high, and interference would be an issue. It might not break the squelch (spread spectrum, etc), but the bits would be corrupted. I see a lot of users on that band, with just a junkbox antenna and